1. Field of the Invention
This invention relates to a process for preparing a high molecular weight organopolysiloxane by use of a hydroxyl-containing organosiloxane as a starting material.
2. Description of the Prior Art
Methods of lengthening the molecular chain of hydroxyl-containing organosiloxanes by use of various silane compounds have been known.
For instance, U.S. Pat. No. 3,776,934 discloses a method in which methylvinylbis(N-methylacetamido)silane is reacted with an organopolysiloxane blocked by hydroxyl group at both ends thereof to form a silicone elastomer composition which is curable at room temperature.
Also, Japanese Patent Publication No. 55-49623 (1980) discloses a method of obtaining a hydroxyl-containing organosiloxane with an increased molecular weight by mixing a hydroxyl-containing organosiloxane with methylvinylbis(e-caprolactamo)silane.
Furthermore, Japanese Patent Publication No. 61-12932 (1986) discloses a method in which a hydroxyl-containing organosiloxane, a cyclosiloxane having two vinyloxy groups bonded thereto and a guanidine derivative are mixed together to form a hydroxyl-containing organosiloxane with an increased molecular weight.
According to the above methods of the prior art, however, an amide or caprolactam having toxicity or odor is by-produced or there is need to use a cyclosiloxane which is difficult to synthesize. Therefore, the methods of the prior art are not so high in practicability.
It is disclosed in U.S. Pat. No. 3,155,634 that a polyorganosiloxane with an increased molecular weight is obtainable by condensation of siloxanes in the presence of a fluorine-containing aliphatic carboxylic acid as a condensation catalyst. However, such a fluorine-containing aliphatic carboxylic acid as disclosed in the U.S. patent is low in capability as condensation catalyst. Therefore, the method disclosed in the U.S. patent has the disadvantage that the condensation reaction must be carried out at high temperature for a long time, and has problems yet to be solved before the method can be used, particularly for preparation of high molecular weight organopolysiloxanes.